The invention pertains to the field of construction, in particular, of building oil and gas wells, and can be used for casing stings and tubings. A threaded joint for casing strings and tubings is highly-tight and is designed for use in wells characterized by high rates of shaft crookedness and/or severe operating conditions, such as high tension or compression loads, excessive internal and external pressures, and environments with high concentrations of H2S and CO2.
Known is a technical solution protected by patent FR 1489013, priority Nov. 5, 1965, describing a highly-tight threaded joint. In the known technical solution, the threaded joint has internal and external interfacing elements with tapered surfaces. The tapered surfaces of the elements have threads with a bearing face and an inserted face. On the side of the thread taper's smaller diameter, there is a sealing component made in the shape of a wedge and comprising parts of the internal element and external element.
However, a shortcoming of this threaded joint is that the sealing component is not sufficiently tight. In addition, such a design makes it impossible to achieve the desired interference at low axial movements of the internal element, which lengthens the time between the first contact of the sealing surfaces and achievement of the required interference. In addition, under severe operating conditions (high tension or compression loads, excessive internal and external pressures) there are flexural deformations that disrupt the contact of taper surfaces which results in unsealing the threaded joint.
This technical solution is used as the closest analogue of the claimed technical solution.
In developing the invention, the objective was to design a highly-tight threaded joint that would make it possible to reassemble the threaded joint without damaging it, ensuring extreme tightness, improving the behavior of the threaded joint in tension and bending, achieving a guaranteed contact along the straight section of the thread bearing surface when screwing and unscrewing the joint, and increasing resistance to compression loads.
The achieved technical is increased reliability and tightness of the joint, increased joint strength, simplified assembly-disassembly during operation, and increased wear resistance and life of the joint.
This technical result is achieved due to the fact that a highly-tight threaded joint has internal and external interfacing elements with tapered surfaces that have threads with bearing and inserted faces, and on the side of the thread taper's smaller diameter, there is a sealing component made in the shape of a wedge and comprising parts of internal and external elements. The sealing component's internal and external parts are formed by a tapered radial surface and a tapered bearing surface, wherein the tapered radial surface is at a 25°-35° angle to the normal to the thread axis, and the tapered bearing surface is at a 10°-25° angle to the normal to the thread axis.
The table vividly demonstrates the effect of the angles on the threaded joint's tightness, reliability and life. The table's second column shows the pressure a pipe and joints must withstand while maintaining tightness. The third and fourth columns show stress readings taken when testing the joint; in the process, the joint itself had remained tight.
Average ContactAverage ContactStresses in theStresses in theAngleHydrotestingRadial Seal AfterRadial Seal AfterCombinationPressure, MPaAssembly, MPaTension (0.8στ), MPa25°-10°64.5793.7690.230°-15°1054.9794.335°-25°1158.5865.1
These features are essential and interrelated, forming a stable set of essential features that is sufficient to achieve the stated technical result.
In the sealing component, contact between the radial seal of the part of the internal element in the shape of a cone, and the mating tapered surface of the part of an external element, takes place with interference over a relatively small area. As a result, high contact stresses occur which ensures high tightness. The rapid achievement of the desired radial interference during the assembly process results in a design that makes it possible to reassemble the threaded joint without damaging the sealing surface. In addition, such design of the sealing component makes it possible for the threaded joint to stay tight when exposed to substantial flexural loads. As a result, the bearing surfaces protect the radial seal from excessive torque and compression.
To enhance the technical result, one can use a series of the following features.
In the highly-tight threaded joint, thread with a 1:16 taper is used.
The thread bearing face is at a 1°-5° angle to the normal to the thread axis, and the inserted face is at a 7°-25° angle. This angle of the thread bearing face ensures improved operation of the threaded joint in tension and bending, and the angle of the inserted face improves conditions for joint assembly when engaging the first several turns of the thread.
Along the bearing face's straight section, the internal and external parts have different thread radii. Such design makes it possible to improve the threading of the joint together, and increase its resistance to wear and compression loads.